Pulse-driven Josephson digital/analog converter [voltage standard]

The authors have designed and demonstrated a pulse-driven Josephson digital/analog converter. When used as a programmable voltage standard, this device can synthesize metrologically accurate ac waveforms as well as stable dc voltages. We show through simulations that Josephson quantization produces a nearly ideal quantization noise spectrum when a junction is driven with a typical waveform produced by a digital code generator. This technique has been demonstrated in preliminary experiments with arrays of 1000 junctions clocked at frequencies up to 6 Gb/s, where sine waves of a few millivolts in amplitude were synthesized at frequencies up to 1 MHz.